The present invention relates to a temperature control system for semiconductor process chambers.
Temperature control systems are used to monitor and control the temperature of semiconductor process chambers which are used to deposit or etch dielectric and conducting material on semiconductor substrates. The deposition, and etching processes are often highly temperature dependent. For example, in etching processes, the shape of the etched features can widely vary as a function of the temperature profile across the substrate surface which in turn is dependent on the temperature of the chamber surfaces. Also, an etchant byproduct residue layer that forms on walls of the chamber, can flake off and contaminate the substrate when subjected to large thermal stresses arising from temperature variations of the chamber surfaces. Another temperature control problem occurs for chamber walls composed of ceramics such as silicon, B.sub.4 C or BN, which have a relatively low thermal shock resistance and can crack when subjected to high thermal stresses. Also, chamber walls composed of ceramic and metals which have widely varying thermal expansion coefficients can break apart when subjected to different temperatures. Thus, it is desirable to control the temperature of the chamber surfaces and reduce temperature fluctuations from one process cycle to another.
Conventional temperature control systems for semiconductor process chambers include "water-jacket" liquid recirculating systems, radiant heating systems, forced-air cooling systems, or combinations thereof. However, in typical chambers, the arrangement of components such as inductor coils adjacent to the walls of the chamber make it difficult to control the temperature of the chamber surfaces because it is difficult to provide uniform heat transfer rates between the complex shaped features of the inductor coil. Furthermore, conventional water-jacket systems recirculate water through a large number of cooling channels that form a bulky shape surrounding the chamber. Also, the cooling channels absorb RF induction energy and cannot be used in plasma chambers where RF energy has to be coupled to the chamber through spaces in the cooling system. Furthermore, improper positioning of the cooling channels around the components of the chamber can cause localized hot spots and resultant process instabilities. It is also difficult to obtain uniform heat transfer rates across a chamber surface using the cooling channels because they are hard to attach onto convoluted surfaces and form localized thermal resistances at their interfaces.
Forced air cooling systems, as described in U.S. Pat. No. 5,160,545, issued Nov. 3, 1992, use fans to blow air through a heat exchanger and across the chamber surfaces. The forced air systems interfere less with operation of chamber components, such as inductor coils, than water jacket liquid recirculating systems. However, portions of the chamber surface that are shielded by the chamber components result in localized hot spots. Also, because the primary mode of heat transfer is conduction by air, forced air systems typically require extremely large air flow rates to achieve a moderately acceptable response time to temperature fluctuations caused by turning on and off the plasma or other such heat loads. Large air flow rates are only provided by large sized fans which are prone to mechanical failure, and upon failure, can severely damage chamber components and brittle ceramic surfaces.
Thus, it is desirable to have a temperature control system that is capable of providing uniform temperatures across a surface of a process chamber and that can rapidly compensate for temperature fluctuations of the chamber surface. It is further desirable for the temperature control system to provide constant temperatures for widely varying heat loads inside the chamber. It is also desirable to have a temperature control system that does not interfere with the operation of high voltage electrical components, and in particular, does not attenuate the inductive coupling of RF energy coupled through the chamber walls. It is further desirable for the temperature control system to reduce thermal and mechanical stresses on the chamber surfaces.